S.O.S PROBLEMS COMUNICANTING EXTERNAL PROCESSES IN JAVA UNDER LINUX

Question

I've programmed a little program in C called "cinterpreter" which works like
an interpreter, when it launches it shows a welcome message to the display
(standart output), then is always waiting for strings from the keyboard
showing the length of the input strings until the "quit" string is received,
in that case the C program named "cinterpreter" finish, here we can see the
code:
# include <stdio.h>
# include <string.h>
# include <stdlib.h>
char presentacion[8][80] = {
" ||||||||||||||||||\n",
" --- Welcome to Maude ---\n",
" ||||||||||||||||||\n",
" Maude version 1.0.5 built: Apr 5 2000 15:56:52\n",
" Copyright 1997-2000 SRI International\n",
" Thu Aug 9 13:40:25 2001\n",
" \n",
" \n"};
void longitud(char * cadena)
int t;
for(t=0;t<3;t++)
printf("MAUDE_OUT> la cadena %s tiene %d caracteres\n",cadena,strlen(cadena));
fflush(stdout);
int main()
char cadena[80];
int i;
char ch;
for(i=0;i<8;++i) printf("%s",presentacion);
printf("\n");
fflush(stdout);
do {
printf("Press any key to continue\n");
scanf("%c",&ch);
printf("%c\n",ch);
fflush(stdout);
}while (ch != 'q');
printf("\n");
while( strcmp(cadena,"quit") !=0)
printf("\nMAUDEENTRADA>");
fflush(stdout);
scanf("%s",cadena);
longitud(cadena);
I'm intereted in running this program, control it's standart input and
starndart output through a java program through the Runtime , process class
and the correponding methods like "exec", getInputStream, getOutputStream,
getErrorStream, the question is that I do not Know what I'm doing wrongly but
I don't get what I want, I'm interested in sending input to the C subprocess
thorugh its stdin getting it by getoutputStream method, and then read its
answer from its stdout getting it by getoutputStream, then question is that I
can sent de first string and read the first answer but I can't repeat it
again, and I would like to begin a dialog with the subprocess so I need to
send many messages and receive its answer to it, but many times, not just one,
by the moment I got it but just one, if any body can help with this please
answer the question or send any answer to the next adresses
e-mail:
[email protected]
[email protected]
*************** java code **********************
import java.io.*;
public class mioss {
static String proceso = "/bin/cinterprete";
static Process p = null;
//--------- input writting method -----------
static void escribe(OutputStream procesoescribe, String s) {
BufferedWriter laentrada = new BufferedWriter(new
OutputStreamWriter(procesoescribe));
try{
laentrada.write(s + "\n");
laentrada.flush();
}catch(IOException e) {System.out.println("error de escritura");}
//----------- output reading method ---------------
static void leesalida(InputStream procesosalida){
String l;
BufferedReader lasalida = new BufferedReader(new
InputStreamReader(procesosalida));
try{
while ((l = lasalida.readLine()) != null){
System.out.println(l);
} catch(IOException e) {System.out.println("error de readline");}
//------------- reading error method --------------------
static void leerror(Process p){
String l;
BufferedReader elerror = new BufferedReader(new
InputStreamReader(p.getErrorStream()));
try{
while ((l = elerror.readLine()) != null){
System.out.println(l);
elerror.close();
} catch(IOException e) {System.out.println("error de readline");}
//--------------- principal method main -------------------------
static Process proc = null;
public static void main(String [] Args) {
try{
Runtime r = Runtime.getRuntime();
proc = r.exec(proceso);
escribe(proc.getOutputStream(),"map(+2)[3,3]");
leesalida(proc.getInputStream());
escribe (proc.getOutputStream(),"map(*3)[2,2]");
leesalida(proc.getInputStream());
}catch(Exception e) {System.out.println("error de ejecucion del
proceso");}
System.out.println("THE END OF THE PROGRAM");

Answer 1

The problem is with the leesalida method.
There you are reading form the output sream of the process usingBufferedReader.readLine.
readLine returns null only when it gets to the end of the stream, or here the stream ends only when the external processes ends.
You can modify your code like this:
public class mioss {
    static String proceso = "cinterprete";
    static Process p = null;
    //--------- input writting method -----------
    static void escribe(OutputStream procesoescribe, String s) {
     BufferedWriter laentrada = new BufferedWriter(new
         OutputStreamWriter(procesoescribe));
     try{
         laentrada.write(s + "\n");
         laentrada.flush();
     }catch(IOException e) {System.out.println("error de escritura:" + e);}
    //----------- output reading method ---------------
    static void leesalida(InputStream procesosalida, int nLines){
     String l;
     BufferedReader lasalida = new BufferedReader(new
         InputStreamReader(procesosalida));
     try{
         while(nLines-- > 0) {
          l = lasalida.readLine();
                System.out.println("from java:\t" + l);
     } catch(IOException e) {System.out.println("error de readline");}
    //------------- reading error method --------------------
    static void leerror(Process p){
     String l;
     BufferedReader elerror = new BufferedReader(new
         InputStreamReader(p.getErrorStream()));
     try{
         while ((l = elerror.readLine()) != null){
                System.out.println(l);
         elerror.close();
     } catch(IOException e) {System.out.println("error de readline");}
    //--------------- principal method main -------------------------
    static Process proc = null;
    public static void main(String [] Args) {
     try{
         Runtime r = Runtime.getRuntime();
         proc = r.exec(proceso);
         leesalida(proc.getInputStream(), 9);
         escribe(proc.getOutputStream(),"first");
         leesalida(proc.getInputStream(), 4);
         System.out.println("Done first !\n");
         escribe (proc.getOutputStream(),"second");
         leesalida(proc.getInputStream(), 4);
         System.out.println("Done second !\n");
     }catch(Exception e) {System.out.println("error de ejecucion del proceso");}
     System.out.println("THE END OF THE PROGRAM");
} Regards,
Iulian